Plague, NIAID Fact Sheet, February 2003

February 2003

Plague

Overview

Plague is an infectious disease caused by the bacterium Yersinia pestis. The bacterium is found mainly in rodents, particularly rats, and in the fleas that feed on them. Other animals and humans usually contract plague from rodent or flea bites.

Historically, plague decimated entire civilizations. In the 1300s, the "Black Death," as it was called, killed approximately one-third (20-30 million) of Europe's population. In the mid-1800s, it killed 12 million people in China. Today, thanks to better living conditions, antibiotics, and improved sanitation, there are only about 1,000 to 3,000 cases a year worldwide.

Transmission

Yersinia pestis is found in animals throughout the world, most commonly in rats but occasionally in other wild animals, such as prairie dogs. Most cases of human plague are caused by bites of infected animals or the infected fleas that feed on them. In almost all cases, only the pneumonic form of plague (see below) can be passed from person to person.

Forms of Plague

Only one plague bacterium causes plague, but it can infect people in three different ways.

Bubonic plague

In bubonic plague, the most common form, plague bacteria infect the lymph system.

How is it contracted? Most people contract bubonic plague either by being bitten by an infected flea or rodent. In rare cases, Y. pestis bacteria enter through an opening in the person's skin, from a piece of contaminated clothing or other material used by a person with plague.

What are the symptoms? Bubonic plague affects the lymph nodes. Within 2 to 6 days of exposure to the bacteria, an infected person develops fever, headache, chills, weakness, and swollen, tender lymph glands (called buboes-hence the name bubonic).

Is it contagious? Bubonic plague is rarely spread from person to person.

Septicemic plague

This form of plague occurs when the bacteria multiply in the blood.

How is it contracted? Septicemic plague is contracted the same way as bubonic plague-usually through a flea or rodent bite. Septicemic plague also can appear as a complication of untreated bubonic or pneumonic plague.

What are the symptoms? Symptoms include fever, chills, weakness, abdominal pain, shock, and bleeding underneath the skin or other organs. Buboes, however, do not develop.

Is it contagious? Septicemic plague is rarely spread from person to person.

Pneumonic plague

This is the most serious form of plague and occurs when Y. pestis bacteria infect the lungs and cause pneumonia.

How is it contracted? Pneumonic plague occurs two ways.

Primary pneumonic plague occurs when a person inhales the plague bacteria. This type of plague can be spread from person to person, or animal to person, through the air.
Secondary pneumonic plague occurs when a person with untreated bubonic or septicemic plague develops pneumonic plague after the disease spreads internally to their lungs. At this point, the disease can be spread person to person.

What are the symptoms? Within 1 to 3 days of exposure to airborne droplets of pneumonic plague, people develop fever, headache, weakness, and rapidly developing pneumonia with shortness of breath, chest pain, cough, and sometimes bloody or watery sputum.

Is it contagious? Pneumonic plague is contagious. When someone with pneumonic plague coughs, they release Y. pestis bacteria suspended in respiratory droplets into the air. If an uninfected person breathes in the droplets, they can develop pneumonic plague.

Diagnosis

Health care workers can diagnosis plague by doing laboratory tests on blood or sputum or on fluid from a lymph node.

Treatment

When the disease is suspected and diagnosed early, health care workers can treat people with plague with specific antibiotics, generally streptomycin or gentamycin. Certain other antibiotics are also effective. Left untreated, bubonic plague bacteria can quickly multiply in the bloodstream, causing septicemic plague, or even progress to the lungs, causing pneumonic plague.

Prevention

Antibiotics

Health experts recommend antibiotics for people exposed to wild rodent fleas during a plague outbreak in animals, or to a possible plague-infected animal. Because there are so few cases of plague in the United States, experts do not recommend taking antibiotics unless the person is certain that he or she has been exposed to plague-infected fleas or animals.

Vaccine

Currently, there is no commercially available vaccine against plague.

How Common Is Plague?

Approximately 10 to 20 people in the United States develop plague each year from flea or rodent bites-primarily infected prairie dogs-in rural areas of the southwestern United States. About 1 in 7 of those infected die from the disease. There has not been a person-to-person infection in the United States since 1924.

Worldwide, there have been small plague outbreaks in Asia, Africa, and South America.

Plague and Bioterror

Bioterrorism is a real threat to the United States and around the world. Although the United States does not currently expect a plague attack, it is possible that pneumonic plague could occur via an aerosol distribution. The Y. pestis bacterium is widely available in microbiology banks around the world, and thousands of scientists have worked with plague, making a biological attack with the disease a serious concern.

NIAID Research

The National Institute of Allergy and Infectious Diseases (NIAID), is part of the National Institutes of Health, an agency of the U.S. Department of Health and Human Services. NIAID supports research on the diagnosis, prevention, and treatment of infections caused by microbes, including those that have the potential for use as biological weapons. The research program to address biodefense includes both short- and long-term studies targeted at designing, developing, evaluating, and approving specific tools (diagnostics, therapies, and vaccines) needed to defend against possible bioterrorist-caused disease outbreaks.

Current research projects include

Identifying genes in the Y. pestis bacterium that infect the digestive tract of fleas and researching how the bacterium is transferred to humans
Studying the disease-causing proteins and genes of Y. pestis that allow the bacterium to grow in humans and how they function in human lungs

NIAID is also working with the Department of Defense, the Centers for Disease Control and Prevention, and the Department of Energy to

Develop a vaccine that protects against inhalationally acquired pneumonic plague
Develop promising antibiotics and intervention strategies to prevent and treat plague infection

More Information

National Institute of Allergy and Infectious Diseases
National Institutes of Health
31 Center Drive, MSC 2520
Bethesda, MD 20892-2520
http://www.niaid.nih.gov

National Library of Medicine
MEDLINEplus
8600 Rockville Pike
Bethesda, MD 20894
1-800-338-7657
http://www.nlm.nih.gov/medlineplus

U.S. Centers for Disease Control and Prevention
1600 Clifton Road
Atlanta, GA 30333
1-888-232-3228
http://www.bt.cdc.gov/

Johns Hopkins University Center for Civilian Biodefense Studies
http://www.hopkins-biodefense.org/pages/agents/agentplague.html

NIAID is a component of the National Institutes of Health (NIH), which is an agency of the Department of Health and Human Services. NIAID supports basic and applied research to prevent, diagnose, and treat infectious and immune-mediated illnesses, including HIV/AIDS and other sexually transmitted diseases, illness from potential agents of bioterrorism, tuberculosis, malaria, autoimmune disorders, asthma and allergies.

News releases, fact sheets and other NIAID-related materials are available on the NIAID Web site at http://www.niaid.nih.gov.

Prepared by:
Office of Communications and Public Liaison
National Institute of Allergy and Infectious Diseases
National Institutes of Health
Bethesda, MD 20892

Department of Health
and Human Services

National Institutes of Health (NIH)
Bethesda, Maryland 20892

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Last Updated June 02, 2003 (alt)